The HEAO-1 Satellite

Beginning in 1977, NASA launched a series of
very large scientific payloads called High Energy Astronomy
Observatories(HEAO). The first of these missions, HEAO-1 surveyed the
X-ray sky almost three times over the 0.2 keV - 10 MeV energy band,
provided nearly constant monitoring of X-ray sources near the ecliptic poles.
More detailed studies of a number of objects were made through pointed
observations lasting typically 3-6 hours.